In reply to Flat4matt: It depends how much money you have. AMD has more bang for a lower cost, but if you can afford an i5 and above then intel is the way to go.
However this could all change if the people who make the programs like lightroom, photoshop, start to better optimize their program for hyerthreading or 8 cores. You also need an os that can do this.
AMDs first 4,6,8 core 41xx 61xx and 81xx series were hitting the benchmarks of their previous Phenom proc, but the new 43xx.. is suposed to be much much better.
Save money on the procc and get more ram and a ssd. You can have a silly fast cpu, but its pointless if you cant get the data off your hdd fast enough. Dont forget to check your OS and hardware can take the extra ram. I have a friend who upped his mac to 16gb, but the apple webstite showing how to change the ram (which he posted on fb), says the max is 8gb. Dont know if he knows this. It was faster anyhow, but only half of his £120 of ram could have been in use.